No, that does not help, besides saying that Model.all has changed. Okay, Model.all now returns something different (a relationship, rather than a collection of records) but why the deprecation warning?

I agree with dowdrake. I think there is something going on with your setup. I am using 4.0 and am using Model.all without any issue. I also assume that you are following the upgrade guide to make sure everything is in order (as best as possible)?

Not sure what version of rails your upgrading from but maybe these will help: